The present invention pertains generally to hybrid microcircuits and more specifically to thin film resistive networks.
The conventional manner of attaching electrical contacts to hybrid thin film resistors formed from chromium-silicon oxide has been to evaporate and etch aluminum or other metal pads directly to the chromium silicon oxide material. During this processing, a thin oxide film has typically formed on the surface of the chromium-silicon oxide prior to depositing the aluminum which has prevented a uniform low resistance contact between the aluminum pad connectors and the chromium-silicon oxide material. This inexact method of attaching the aluminum or other metal pad connectors to the resistive material has resulted in the existence of unstable conditions upon application of voltage to the connection or variations in temperature conditions near the connector junction. The potential for these instabilities has reduced the reliability of resistive networks fabricated in this manner.
Another problem which has also developed in generation of thin film resistive networks is the production of a high precision trimmable resistor. It has been found that certain patterns of resistive films can be etched away by lasers or other etching devices to produce a thin film resistor having a desired resistivity. However, high precision in obtaining this resistivity has not been possible due to the nature and manner of the resistive films and method of cutting, respectively. Moreover, the generation of multiple resistive networks wherein the specific resistive elements vary greatly in magnitude has not been possible in an exacting manner with a single resistive material. Since a practical method of using more than one resistive material in a simplified manner has heretofore not been available, other more complex methods were required to obtain greater precision.